How to determine if PDO enabled in PHP
if (class_exists('PDO'))

if ( extension_loaded('pdo') ) {
    .......
}

if ( extension_loaded('pdo_<database type here>') ) {
    .......
}

if (extension_loaded('pdo')) { /* ... */ }

if (class_exists('PDO', false)) { /* ... */ }

if (in_array('pdo', get_loaded_extensions())) {
   ... pdo is there ...
}

if (!defined('PDO::ATTR_DRIVER_NAME')) {
echo 'PDO unavailable';
}
elseif (defined('PDO::ATTR_DRIVER_NAME')) {
echo 'PDO available';
}